[Windows] Create a certbot renew scheduled task using the installer (#7371)

This PR implements the item "register a scheduled task for certificate renewal" from the list of requirements described in #7365.

This PR adds required instructions in the NSIS installer for Certbot to create a task, named "Certbot Renew Task" in the Windows Scheduler. This task is run twice a day, to execute the command certbot renew and keep the certificates up-to-date.

Uninstalling Certbot will also remove this scheduled task.

* Implementation

* Corrections

* Update template.nsi

* Improve scripts

* Add a random delay of 12 hours

* Synchronize template against default one in pynsist 2.4

* Clean config of scheduled task

* Install only in AllUsers mode

* Add comments

* Remove the logic of single user install

windows-installer/renew-down.ps1

@@ -0,0 +1,6 @@
+$taskName = "Certbot Renew Task"
+
+$exists = Get-ScheduledTask | Where-Object {$_.TaskName -like $taskName}
+if ($exists) {
+    Unregister-ScheduledTask -TaskName $taskName -Confirm:$false
+}